What was Mastema's plan in SMT4?

[Marc]

There is a quest to slay Mastema in Shin Megami Tensei IV when you're far in the game.

Spoiler: Pic of Masterma in SMT4

You meet him once or twice (I think) in the game and he kind of looked surprised to see you the first time you encounter him in the game. According to him, he "let you off easy" the first time, but I'm wondering what his plans were.

He was underground and he didn't really seem to have the motive of betraying his god >.<

Does anyone else know what his plans were or have an idea what his plans were?

 

[Theresia]

If I remember correctly, Mastema's true intentions are revealed only in the 2 DLCs "Clipped Wings".
If you plan to purchase them, you'll be revealed his plan by completing them, but if you don't want to buy anything, open the following spoiler:

Spoiler

In Clipped Wings you're teleported back in the past, during Aquila's age, and you'll meet your committent, M, who is Mastema in disguise, he'll ask you to get rid of the four Archangels, because they aren't following God's plan and trying to achieve power for their own personal desires: their only role was to simply help men creating the Kingdom of Mikado and then simply observe them, but they instead tried to take over Tokyo and wiping out humanity.
So, you're sent to Tokyo and are tasked to defeat Uriel and Raphael in the first DLC, in the latter Micheal and Gabriel, IIRC.
When you beat each pair, aside from unlocking the Archangels' Special Fusion, Mastema will put on a mask on the defeated foes' faces to cancel their memories and lock them up - in birdcages - in a certain tower in Tokyo...
That's why, after being fred, the Archangels want Mastema dead.